In the face of ever-tightening sulfur specifications in transportation fuels, sulfur removal from petroleum feedstocks and products will become increasingly important in years to come. While diesel oil's sulfur specification in the U.S. has recently been lowered to 0.05 wt %, indications are that future specifications may go far below the current 0.05 wt % level. Conventional hydrodesulfurization (HDS) catalysts can remove a major portion of the sulfur from diesel fuels, but they are not active for removing the so called "hard sulfur"--the sulfur that is sterically hindered in the multiring aromatic sulfur compound. This is especially true where the sulfur heteroatom is doubly hindered (e.g., 4,6-dimethyldibenzothiophene or 4,6-DMDBT for short). In order to meet stricter specifications in the future, this hard sulfur will also have to be removed from distillate feedstocks and products. There is a pressing need for economical removal of sulfur from distillates and other hydrocarbon products.
One may view the conventional HDS process as a separation device for removing easy sulfurs and multiring aromatics. Easy sulfurs include non-thiophenic sulfur, thiophenes, benzothiophenes, and dibenzothiophenes in which the substituents are away from the sulfur heteroatom. Multiring aromatics in the conventional HDS process are mostly reduced to mononuclear aromatics (e.g., tetralins). Thus, the need essentially is that of removing hard sulfurs from a "sea" of mononuclear aromatics. The present invention addresses this pressing need.